1. Field of the Invention
The present invention relates to a fine spherical silica having excellent viscosity characteristics and a liquid sealing resin composition for sealing slight gaps between a substrate and an IC chip.
2. Description of Related Art
Demand for high performance and functionality in electronic equipment is increasing with the advent of the multimedia age. In view of this, the shape of IC packages used in electronic equipment tends to be small, thin and of a multiple pin structure. Semiconductor chips are molded by sealing the entire IC chip with an sealant in order to protect fine and complicated electronic circuits formed on the surface thereof from dust or moisture in the air. At present, the material that is most commonly used as an sealant for semiconductor IC chip, is an epoxy resin sealant. This epoxy resin sealant is roughly classified into an epoxy resin sealant for transfer molding and a liquid epoxy resin sealant. The sealant mainly used at present is the epoxy resin sealant for transfer molding, and the use of liquid epoxy resin sealant has heretofore been limited.
However, recently this liquid epoxy resin sealant is beginning to be used as an sealant for the most advanced semiconductor devices, for example, P-PGA (Plastic Pin Grid Array), P-BGA (Plastic Ball Grid Array), flip chip or CSP (Chip Size Package or Chip Scale Package). Of these, many CSPs have a smaller and more complicated structure than conventional devices. The gaps between a substrate and an IC chip in CSPs have been conventionally about 75 to 100 xcexcm. However, in recent years, bump size has become small due to the narrow pitch resulting from a multiple pitch structure, and devices having gaps of about 30 to 50 xcexcm are becoming more common. Further, in the most advanced semiconductor devices, devices having a gap size of 1 mil (25.4 xcexcm) are being developed.
In order to seal these very advanced semiconductor devices, a fine process-ability is required, and as a sealant which can meet this requirement, there has been a demand for development of a liquid epoxy resin sealant having excellent gap permeability.
On the other hand, the conventional liquid epoxy resin sealants have a problem in that stress generated due to difference between the coefficients of linear expansion of the liquid sealant and an IC chip need to be reduced in order to increase the reliability of the sealant. As a method for solving this problem, there is a method of decreasing the coefficient of linear expansion by blending a large amount of silica filler in the liquid epoxy resin sealant, and as a method for solving the problem of fluidity due to this blend of large amount of silica filler, many methods have been proposed in which finely fused spherical silica having excellent low viscosity characteristics is used (for example, Japanese Patent Application Laid-open Nos. Hei 2-59416, and Hei 2-199013).
However, it is difficult to say that conventional liquid epoxy resin sealants have high reliability together with the capability of holding a large amount of silica filler, as well as sufficient gap permeability for sealing slight gaps between a substrate and an IC chip in the most advanced semiconductor devices. For this reason, there has been a demand for development of a liquid epoxy resin sealant having high reliability together with the capability of holding a large amount of silica filler as well as excellent gap permeability, and a silica for a liquid sealant, which imparts this performance from the silica filler side.
Accordingly, an object of the present invention is to provide a liquid sealing resin composition having excellent gap permeability for sealing slight gaps between a substrate and an IC chip and also having high reliability, and a fine spherical silica filler to be filled therein.
In view of the above, the inventors of the present invention have made extensive investigations, and found that the above conventional problems can be overcome, and excellent gap permeability for sealing slight gaps between a substrate and an IC chip and high reliability can be obtained, if fused spherical silica having specific particle size characteristics and viscosity characteristics, for example, a fine spherical silica obtained by mixing fine particles with relatively large particles in a specific proportion, is blended with an epoxy resin or silicone resin which is liquid at room temperature. The present invention has been completed based on this finding.
That is, the present invention provides a fine spherical silica having a particle size distribution in which a maximum particle diameter is 24 xcexcm, an average particle diameter is 1.7 to 7 xcexcm, and a proportion X1 of particles having a particle diameter of 3 xcexcm or less in the total particles is in a range from 100/D50 wt % to (18+100/D50) wt %, characterized in that viscosity at 50xc2x0 C. of a mixture obtained by blending a maximum of 80 wt % in terms of the total weight amount of the fine spherical silica with epoxy resin or silicone resin which is liquid at room temperature is 20 Paxc2x7s or less.
Further, the present invention provides a fine spherical silica, characterized by comprising a mixture of (A) fused spherical silica having a particle size distribution in which a maximum particle diameter is 24 xcexcm, an average particle diameter is 2 to 7 xcexcm and a proportion of particles having a particle diameter of 1 xcexcm or less in the total particles is 1 wt % or less, and having a BET specific surface area of 3 m2/g or less, and (B) spherical silica having a maximum particle diameter of 10 xcexcm, an average particle diameter of 0.3 to 1.0 xcexcm and a BET specific surface area of 6 to 15 m2/g, the weight ratio of (A)/(B) being in a range of 99/1 to 40/60.
Still further, the present invention provides a liquid sealing resin composition comprising an epoxy resin or silicone resin which is liquid at room temperature and 30 to 80 wt % of the fine spherical silica blended therewith.
Even if the fine spherical silica filler for a liquid sealant of the present invention is blended in large proportion with an epoxy resin or silicone resin, which is liquid at room temperature, the viscosity is not lowered and the coefficient of linear expansion of the liquid sealing resin composition can be minimized. Therefore, the fine spherical silica filler can impart high reliability. Further, even if the fine spherical silica filler is blended in large proportions, the resulting liquid sealing resin composition has low viscosity, and therefore, good gap permeability.